A color liquid-crystal display unit is constituted by from several hundreds of thousands of pixels to several millions of pixels and each pixel is constituted by subpixels of three primary colors (RGB) of red, green, and blue. The liquid-crystal color display unit is divided into a color filter liquid-crystal display unit using color filters of RGB in order to display RGB every subpixel and a color-filterless liquid-crystal display unit not using color filters.
The following documents are considered:                [Patent Document 1] Published Unexamined Patent Application No. 2000-241812        [Patent Document 2] Published Unexamined Patent Application No. 9-127331        [Patent Document 3] Published Unexamined Patent Application No. 2000-56105        [Patent Document 4] Published Unexamined Patent Application No. 2000-84995        
FIG. 19 shows a color-filterless liquid-crystal display unit (refer to Patent Document 1). The display unit shown in FIG. 19 is constituted by a linear or planar light source 100, a wedge-shaped light guide plate 101 into which the light emitted from the light source 100 comes, wavelength dividing means 102 for dividing the light emitted from the wedge-shaped light guide plate 101 in the diagonal direction and almost in parallel into lights of a plurality of wavelength regions, condensing means 103 for condensing the lights divided by the wavelength dividing means 102, a liquid-crystal layer 104 capable of controlling a transmissivitiy every subpixel, and a polarization film 105. The display unit shown in FIG. 19 is further provided with a diffusion plate 106 and a reflection sheet 107.
The light emitted from the linear or planar light source enters the wedge-shaped light guide plate 101 and its angle gradually becomes steeper while repeating reflection at the downside and upside of the wedge-shaped light guide plate 101. When the direction of the light exceeds a critical angle at the upside of the wedge-shaped light guide plate 101, the light is emitted at the upside. Because the light is not emitted before the direction of the light exceeds the critical angle, the light is almost parallel light. The light is divided into RGB lights by the wavelength dividing means 102. The divided RGB lights enter the condensing means 103. The condensing means 103 forms a periodic structure and a structure for one period corresponds to one pixel. In the case of the light entering the condensing means 103, red light enters a subpixel R of, green light enters a subpixel G of, and blue light enters a subpixel B of the liquid-crystal layer 104 and transmission or cutoff of light is controlled every subpixel.
In the case of the display unit shown in FIG. 19, diffracted lights of three colors of RGB are emitted at an angle in which blue light and red light are almost bilaterally symmetric centering around green light. Moreover, in the liquid-crystal layer 104, the diffracted lights are entered into openings of subpixels corresponding to each color in a state condensed with the positional translation according to an incident angle by the condensing means 103 having a period corresponding to openings of three subpixels of RGB constituting one pixel. By driving the liquid-crystal layer 104 corresponding to individual subpixel and thereby modulating the intensity of transmitted light, it is possible to display a desired color image. It is possible to perform light diffusion correction and visual field angle correction on the surface of the liquid-crystal layer 104 by using a light diffusion film or transmission-type diffraction-grating film in order to widen a visual field for lights of three wavelengths having different exit angles emitted from the liquid-crystal layer 104 because of a diffraction angle depending on a wavelength. Also in the case of a color-filterless liquid-crystal projection apparatus, because light is separated from a white light source by wavelength dividing means such as a dichroic mirror or diffraction grating and enters a liquid-crystal layer while condensed by condensing means, each light has incident angle conditions in which angles of lights of colors of RGB are different as in the above mentioned apparatus.
In the case of the above described conventional display unit, incident angles of RGB components inputted to openings of three subpixels of RGB are different and angle distributions of lights outputted from subpixels do not coincide with each other in RGB. Therefore, there is a problem that a change of color balances easily occurs depending on a view point for observation. As a result, the liquid-crystal projection apparatus has problems that color mixing occurs, an image is blurred, and the color reproducibility and resolution are deteriorated. Therefore, it is difficult to provide a color image display unit having a large screen.
Moreover, though the above-described light diffusion film scatters and diffuses light to make it possible to obtain an uniform brightness, only the light is obtained which holds the light intensity center even after an liquid-crystal layer exit angle depending on a wavelength passes through the light diffusion film. Therefore, there is a problem that it is difficult to widely secure an angle of visibility superior in color reproducibility and having a uniform color balance.
It is possible to use a transmission-type blazed grating film having a triangular sectional shape by which a high diffraction efficiency can be obtained as a visibility-angle correcting function member. However, there is a problem that it is difficult to design a film for controlling a diffraction efficiency depending on a wavelength and accurately correcting the incoming light angle of every wavelength to an equivalent visibility-angle distribution.
The color reproducibility in the front direction when using a color-filterless direct-viewing liquid-crystal display unit together with the transmission-type diffraction grating film is 38% in the NTSC (video signal system of a generally used television) ratio, which is lower than 42% of a 13.3-type color-filter direct-viewing liquid-crystal display unit. Moreover, when defining condition of angle of visibility in which the chromaticity can be regarded to be uniform as a range in which an error with a front-directional output light component is kept within 0.02 for both chromaticity coordinates x and y (that is, both x coordinate value and y coordinate value in a chromaticity diagram), an exit angle range satisfying the above condition is a narrow range between about −5° and about 7°. Moreover, in the case of the peak value of the brightness in the front direction, the brightness value in the front direction when not using a diffraction grating film is 217 cd/m2 but the brightness value after adding the film is 85 cd/m2 which is attenuated to 40% or lower. Therefore, the transmission-type blazed grating film has a problem that it does not carry out a sufficient visibility-angle correcting function in brightness and chromaticity.
In view of the above problem, by appropriating an optical filter having a multilayer structure obtained by alternately repeating two types of polymer layers formed by applying a linear ultraviolet radiation to a film-like body constituted by two types of ultraviolet curing polymers having different refractive indexes and using that anisotropy is shown at the time of photopolymerization curing with phase separation to a color-filterless liquid-crystal display unit, it is also considered to provide a visibility-angle correcting function (refer to Patent Document 2).
However, because the multilayer structure of the optical filter obtained by alternately repeating two types of polymer layers is formed in a photopolymerization curing process, the optical filter has a problem that it is impossible to form the structure by optionally controlling the sectional shape of each polymer layer, interval between the polymer layers, and tilt angles of the polymer layers and form a structure having a sufficient accuracy necessary for the above visibility-angle control. Moreover, because the difference between refractive indexes of two types of polymers is as small as about 0.02 (about 0.04 even at the maximum), a visibility-angle correction limit under the total reflection condition when using a high-refractive-index polymer layer as a light guide path ranges between −15° and 15° in air and ranges between −20° and 20° even at the maximum. Therefore, there are problems that a correction angle is small and a correction effect is not sufficient. In the case of an optical filter, it is intended to improve the diffusion capacity by almost uniforming a periodic interval for forming two types of polymer layers to set the periodic interval to a short periodic interval of about 2 μm and thereby using a diffraction effect. However, as described above, because it is impossible to perform a sufficient structure control, the diffraction effect is actually hardly obtained and the diffusion capacity is almost decided in accordance with the difference between refractive indexes of polymers.
Moreover, a one-dimensional or two-dimensional periodic-structural device is proposed which is provided with a pillar member having a light transmission characteristic and a pillar member having a light diffusion characteristic (refer to Patent Document 3). In the case of the device, the arrangement period of pillar members arranged at equal intervals ranges between 50 and 150 μm and the aspect ratio which is the ratio of the width of each pillar member to the thickness of the device is 1:1. Therefore, it is possible to convert diffused light into a mixed output light of transmitted light and diffused light and moderate that a displayed image is blurred due to contrast deterioration or diffusion caused by external light reflection. However, because the device has only a general diffusion function, there are problems that diffused light is only added to the circumference of the exit angle of non-diffusion transmitted light but it is impossible to provide correction of angle of visibility and improve the wavelength dependency of an exit angle distribution which depends on a wavelength.
Moreover, as another device, a structure is proposed in which pillar members of resins having low transmissivity or different refractive indexes are formed in a transparent film periodically, that is, at equal intervals and moreover a diffusion layer is added (refer to Patent Document 4). In the case of this device, the period is about 300 μm and the height of a pillar member ranges between 1 and 1.5 mm. The device has features of electively emitting only the light in a certain angle range and excluding moiré fringes produced between an image display unit and the device by a diffusion layer. However, the device selectively transmits only an input light component in a certain angle range corresponding to a tilt angle of a pillar member without angle-converting it but it does not have an angle correction function. Therefore, in the case of a color-filterless liquid-crystal display unit, an optical filter is requested which has optimum visibility-angle correction and diffusion function for a request for correction of angle of visibility.